The present invention relates to impact drive tools, for example, for driving nails, staples, or the like, and is particularly directed to the provision of an arresting device for such impact drive tools.
Impact drive tools of one type are provided with a cylinder having a pressure chamber adapted to be connected to a supply of compressed air by way of an inlet valve. An air chamber is provided for storing compressed air, in order to drive the percussive piston to its rest position following an impact stroke. A rubber-elastic arresting element is provided for locking the percussive piston in its rest position, the lock on the piston being released by the force of compressed air applied to the piston in its impact stroke.
An arresting device of the above type is described, for example, in German Pat. No. 1,288,527. In this arrangement the arresting device is provided with a rubber-elastic holding element which at least partially forms a latch, in order to elastically lock the percussive piston in a rest position.
Due to the nature of the operation of impact drive tools of this type, return forces of varying amplitude act on the percussive piston during the return stroke, the amplitude of the force depending upon the air pressure employed. In order to adapt such tools to required conditions, such as the differing lengths of the nails, and the hardness of wood into which the nails must be driven, the pressure of the compressed air applied to the tool may be changed. Changing of the air supply pressure, however, also changes the pressure of compressed air stored in the air chamber for the return of the percussive piston. As a result, the percussive piston strikes the arresting device, which is employed to arrest the piston over the entire range of its impact speeds, with varying speeds.
When minimum air pressure is employed, an energy surplus is required in order to insure safe engagement of the piston in the latch of the arresting element. When maximum air pressure is employed, this energy surplus may cause the percussive piston to strike the elastic buffer surface of the arresting device at high speeds, and to cause its rebound in such a way that it overcomes the holding force of the latch and drops downwardly in the cylinder to a greater or lesser extent. Consequently, when the next impact is to be triggered off in the tool, there is either no impact at all, or an impact with reduced energy. As a result, the nail or similar object is not driven completely into the workpiece as desired.